This invention relates to a hydraulic motor, and in particular to a hydraulic motor in which the power consumption is reduced when the motor is operating at low load, zero load and/or aiding load conditions.
Hydraulic motors are used in a wide variety of applications. One application is in the control of movement of aircraft flaps and slats. In order to minimise the power consumption of such motors in applications where the load on the motor is variable, it is known to use variable displacement motors. Such motors are relatively expensive, and it is an object of the invention to provide a hydraulic motor which permits a reduction in power consumption and which is of relatively simple form.
According to the present invention there is provided a hydraulic motor arrangement comprising a hydraulic motor arranged to receive a driving fluid through an inlet port, the motor including an outlet port whereby fluid can escape from the motor, and a by-pass line interconnecting the inlet and the outlet ports, a non-return valve being located within the by-pass line and arranged to permit fluid flow from the outlet port to the inlet port but to substantially prevent fluid flow in the reverse direction.
In use, where the motor is operating against a significant load, the fluid pressure at the inlet port will be higher than that at the outlet port, thus the by-pass valve will be closed and the motor will operate in the conventional manner. If the applied load is removed, and instead an aiding or assisting load is applied which drives the hydraulic motor, then the fluid pressure at the outlet port will rise above that at the inlet port, and the non-return valve will open permitting fluid to recirculate through the by-pass line to the inlet port. It will be appreciated that, in such circumstances, the net power consumption of the motor is reduced as the quantity of fluid drawn from the fluid supply line to the return line is reduced.
Where the hydraulic motor is of the bi-directional type, appropriate control valves are conveniently provided to control which of the ports of the motor is used as the inlet port and which of the ports of the motor is used as the outlet port at any given instant, and to maintain the appropriate direction of the non-return valve relative to the motor ports.
A restriction is conveniently provided in the by-pass line.
The restriction may be a variable restriction. A pump may be provided in parallel with the variable restriction, the pump being driven at a speed associated with the speed of operation of the motor and arranged to return fluid towards the inlet port of the motor. The restriction is conveniently controlled in such a manner as to be responsive to the load applied to the motor. In such an arrangement, the restriction is conveniently arranged to provide a high restriction to flow under low opposing load conditions, the pump being arranged to return a significant proportion of the fluid passing through the motor back to the inlet port. As a result, the efficiency of the hydraulic motor arrangement is improved under low load conditions.